The GAfuels Blog is written by two private pilots concerned about the future availability of fuels for piston-engine aircraft: Dean Billing, Sisters, Ore., an expert on autogas and ethanol, and Kent Misegades, Cary, N.C., an aerospace engineer, aviation sales rep for U-Fuel, and president of EAA1114.
In Part I of this series, we reviewed the history of the STCs that allow us to use 91+ AKI octane, ethanol-free autogas in hundreds of different legacy aircraft and engines. Part II described the Anti-Detonation Injection (ADI) system from Petersen Aviation/Air Plains that will enable many aircraft not covered by these STCs to operate on affordable, abundant autogas. In the final part of this series, we’ll describe the many piston aircraft engines that are best run on autogas, not leaded avgas. These fall into three categories: two-stroke engines, auto engine conversions, and newer aviation powerplants that have been designed from the outset to operate on autogas. (An excellent list of engines from all three categories may be found in the World Directory of Leisure Aviation. Only spark-ignition engines are mentioned here, i.e. no diesels.)
The first category, two-stroke engines, are generally the powerplant of choice for trikes, powered parachutes, ultralights/microlights, light rotorcraft, self-launching gliders and other aircraft where the two-stroke engine’s high power/weight ratios are needed. Some of the best-known names in aviation two-strokes are Goebler-Hirth, HKS Aviation, Rotax, Simonini Racing and Solo UL-Kleimotoren. All of these engines are designed to operate on 91+ ethanol-free, lead-free autogas. Some tolerate leaded avgas and low levels of ethanol, but their manufacturers generally recommend ethanol-free, lead-free autogas as the best fuel.
The second category of aviation powerplants are auto engine conversions, in use since the 1920s. The original Pietenpol Aircamper, arguably the first homebuilt to be built in large numbers, was powered by engines taken from Ford Model A and Model T automobiles. The Funk Aircraft Co. of Coffeyville, Kansas, powered its Model B aircraft from 1939 with an engine derived from a Ford model “B” engine.
It goes without saying that auto engine conversions all run well on autogas. Depending on their age, they may or may not tolerate low levels of ethanol. Engines developed since leaded car fuels were phased out in the mid 1970s generally may not be operated with leaded avgas. While most auto engine conversions are found in experimental category airplanes, many have been refined to a high level of sophistication, with reliability and performance comparable to purpose-built aircraft engines. Some of the more popular conversions include those from Aero Conversions (VW), Better Half (VW), Ecofly (Smart), Eggenfellner Aircraft (Subaru & Honda), FlyCorvair (Corvair), Geared Drives (Corvette LS1), Great Planes Aircraft (VW), Limbach Flugmotoren (VW), Sauer Flugmotoren (VW), and Take Off (BMW motorcycle).
The third category of aircraft engines that have been developed from the outset for autogas are a growing number of designs intended primarily for aviation use. By far the most ubiquitous of these are the powerplants found in the rapidly expanding Light Sport Aircraft sector, especially the products from Jabiru Aircraft and Rotax. But these companies are no longer alone: A new wave of autogas-burning, sophisticated aircraft engines have been introduced in recent years from CubCrafters, D-Motor, Rotec, and ULPower, with some developing up to 180 hp. In addition to these, the traditional aircraft engine maker Lycoming has begun to introduce its new iE2 technology-based, FADEC-equipped line of engines that can operate on autogas. Most notable among these are the 116-hp IO-233-LSA and the 350-hp TEO-540-A1A. Proof that autogas is fully capable of powering large, modern piston-engine aircraft was Tecnam’s recent announcement of the 11-place twin-engine P2012 Traveller, to be powered by a pair of these 350-hp engines resulting in a remarkably low total fuel burn of 30 gph.
Autogas for everyone? Between the existing autogas STCs described in Part I of this series of articles, and the Petersen/AirPlains ADI system described in Part II, it is estimated that well over 90% of all existing piston-engine aircraft could operate on 91+ AKI octane, ethanol-free, lead-free, affordable, plentiful autogas. With a new generation of aircraft engines providing up to 350 hp, the claim of “autogas for everyone” could very well become reality in a few years.